Electric impedances of variable value



y 22, 1962 L. HALLAS 3,036,263

ELECTRIC IMPEDANCES 0F VARIABLE VALUE 3 Sheets-Sheet 3 Filed July 22,1958 United States Patent 3,036,263 ELECTRIC IMPEDANCES 0F VARIABLEVALUE Lister Hallas, Romford, England, assignor to Telephone CablesLimited, a British company Filed July 22, 1958, Ser. No. 750,197 Claimspriority, application Great Britain July 26, 1957 5 Claims. (Cl. 32374)This invention relates to an improved variable-value impedance of thekind comprising a number of fixedvalue impedances in association with agroup of switches which are operable in sequence to change progressivelythe total value of impedance connected between two terminals. Theinvention also relates to such variable impedances which areautomatically controllable by groups of sequentially actuating relays,similar to relay counters, and can be used, for instance, in theoperation of automatically balancing a bridge network incorporating thevariable impedance in one arm of the bridge. By the term impedance, asused in this specification, is meant impedance which is eithersubstantially capacitative or substantially non-capacitative.

The object of the invention is to provide an impedance which isprogressively variable in steps of equal value over a given range bymeans of an advantageously small number of switches and switchingoperations and which therefore lends itself to being automaticallycontrolled by a correspondingly small number of relays. The inventionwill usually be applied in connection with the decade system of countingbut it is applicable to other systems.

The improved variable impedance in accordance with our inventioncomprises a number of fixed-value impedances associated in sucha mannerwith N two-wayswitches that, by movement of the switches one at a timein succession to the operated condition followed by movement of theswitches one at a time in succession to the non-operated conditions, thevalue of impedance con-' nected between two terminals is progressivelyvariable from a minimum to a maximum value in 2N -1 equalvalue steps bythe first 2N-1 switching operations and is returned to the minimum valueby the next switching operation.

When the impedance is substantially capacitive, the fixed valueimpedances may consist of N -1 single-unitvalue capacitors and oneN-unit-value capacitor with one pole of each capacitor connected to oneof the terminals. The other poles of the single-unit-val-ue capacitorsare separately connected to the movable contact of one of each of N l ofthe switches and the corresponding pole of the N-unit-value capacitor isconnected to the first side contacts of all the switches. In thenon-operated condition of the first N 1 switches, their first sidecontacts are engaged by their movalble contacts. The second sidecontacts of all the switches are connected together and, in itsunoperated condition, the Nth switch completes a circuit from its secondside contact to the other terminal. To vary the capacitance between theterminals from 0 to 2Nl units, in steps of one unit, the first N 1switches are moved to the operated condition one at a time in sequence,the Nth switch is then similarly changed, and thereafter the first N 1switches are returned one at a time in sequence to the non-operatedcondition. By then returning the Nth switch to the non-operatedcondition ice the value of impedance between the terminals is returnedto zero.

Where the imperdance is a variable resistor, it may consist of twoseries connected chains of N1 singleunit-value resistors and, seriesconnected to the end of one chain, one N-units value resistor. Themovable contacts of the first N 1 switches are joined to one terminaland the movable contact of the Nth switch is connected to the otherterminal. One series chain of resistors is connected between thefirst-mentioned terminal and one side contact of the Nth switch, and theother series chain is connected between that terminal and the other sidecontact of the Nth switch, the N-unit-value resistor being at the end ofa chain which is nearest to the Nth switch. The corresponding sidecontacts of the first N --1 switches are connected to one series chainin such a manner that one single-nnit-resistor is connected between eachtwo such side contacts, and the other side contacts are similarlyconnected to the other series chain. The resistors may be replaced byinductances to give a variable inductance.

The switches may be operable by a counting chain of N-relays which areenergisable one at a time in sequence and a subsequently releasable oneat a time in sequence. The relay chain may be of the free-running formin which the relays are energised in the first sequence of oper-a tionsand released during the second sequence. The sequence in which therelays are released may be the same as that inwhichthey are energised orit may be such that the first N -l relays will be released in theopposite order to Which they are energised, the Nth relay being releasedafter the others. The variable capacitor is controllable by eitherarrangement of relays. The variable resistor; or inductance, is made tobe controllable by one system or the other by arranging for the largestresistor to be connected between the side contact of the Nth switch andthe corresponding side contact of the first of the other switches to beoperated by the first released relay.

Where the impedance range extends over several sig-v nificant figures, anumber of the improved variable impedances may be used between twoterminals, one corresponding to each significant figure, and the valuesof the units of impedance are appropriately related in ac cordance withthe requirements of a decade system of counting. Where such anarrangement is relay controlled, a separate relay chain will be providedfor each variable impedance, with means controlled by each relay chainfor initiating a change of state of one step in the next higher chainfollowing the completion of a full cycle of operation of the lowerchain. Where the variable impedance is the variable arm of abridge-network the operation of the relay chain may be under the controlof means which is responsive to the conditions of balance and unbalanceof the bridge. Where the controlling relay system is automaticallyresponsive to the condition of a bridge network, only the lowest valuerelay chain will be free-running with means for arresting the relayoperation at balance. In this case it is preferable to provide means toensure positively that a cycle of operation of the free-running chaincannot begin before the change of state, which is initiated by thecompletion of the previous cycle of that chain, has occurred in one ormore of the higher value relay chains.

The invention Will be further described with reference,-

' 3 by way of example, to the accompanying diagrammatic drawings,wherein:

FIGURE 1 is a circuit diagram of a variable capacitor;

FIGURE 2 is a circuit diagram of a group of relays for controlling thevariable capacitor; and

[FIGURE 3 is a circuit diagram of a variable resistor which is alsocontrollable by a relay group of the form which is represented in FIGURE2.

Each relay is represented in FIGURE 2 by a rectangle containing atwo-letter designation, see for instance relay CA. Except in FIGURE 3,switches which are controlled by each relay are represented by the sametwo letters and a suffix number, for instance, relay CA controls fourswitches CAI-CA4. The relays are adapted to be energised for anyconvenient source of direct current, such as battery, one terminal ofwhich is permanently earthed and one terminal of each relay ispermanently connected to the other terminal the current source which isrepresented by a negative sign in a circle. Each relay is energisable bycompleting a circuit from its other terminal to earth, shownconventionally at the bottom righthand corner of FIGURE 2, that is byputting an earth on a relay. All the switches shown in and describedwith reference to FIGURE 2 will be referred to as relay contacts ormerely as contacts. The switches shown in and described with referenceto FIGURES 1 and 3 will be referred to as switches although they will inpractice also be relay contacts. The switches and contacts are shown inthe unoperated condition, that is to say with all the relaysde-energised.

The variable capacitor represented by FIGURE 1 is designed to providebetween two terminals X and Y a capacitance which is adjustable in unitsteps to any value in the range to 199 units. The instrument is in threesections, referred to as the units, tens and hundreds sections,connected in parallel between the terminals X and Y. It incorporatesfour l-unit condensers Cl and one S-unit condenser C in the unitssection, four IO-unit condensers C and one SO-unit condenser C50 in thetens section, and one IOU-unit condenser C100 in the hundreds section.The units and tens sections are similarly constructed. The terminal X ispermanently connected to one pole of each condenser in the unitssection. The other poles of the unit condensers C1 are connected to themovable contacts of four two-way switches CA4- CD4. In the unoperatedcondition of these switches, the movable contacts close on to their sidecontacts 19 which are permanently connected together, to a side contactb of another two-way switch CBS and to the remaining electrode of theS-unit condenser C5. In the unoperated condition of the switch CES, itsmovable contact is closed on its other side contact a. The terminal Y ispermanently connected to the movable contact of switch CBS, and theremaining side contact a of switch CBS is permanently connected to theremaining side contacts a of switches CA4-CD4. In the unoperatedcondition of the switches, no condenser of the units section isconnected between terminals X and Y.

The tens section is similar to the units section, except as regards thefollowing features. In place of the four l-unit condensers C1 there areprovided four 10-unit condensers C10, and in place of the S-unitcondenser C5 there is provided a 50-unit condenser C50. The five twowayswitches CA4-CD4 and CBS are replaced by similar switches CF4-CI4 andC15. In the unoperated condition of the switches, no condenser of thetens section is connected between the terminals X and Y. The hundredssection consists of a single -100-unit condenser C100 in series with asingle-pole switch CK4 between the terminals X and Y. The switch CK4 isopen in its unoperated condition, so that in that condition theIOOTunitS condenser is not electrically connected to both terminals Xand Y.

The value of the capacitance between the terminals X and Y can be raisedto four units in single unit steps by operating, that is changing overthe moving contacts of, the four switches CA4 to CD4 one at a time andin that order. In that condition the moving contacts of the fourswitches CA4-CD4 are in engagement with their side contacts a. Byoperating the fifth switch CES, the circuit is completed between theterminals X and Y through the S-unit condenser, and the circuit fromterminal Y to the side contacts a of switches CA4-CD4 is broken, so thatalthough the four l-unit condensers C1 are no longer in circuit betweenthe terminals X and Y, the capacitance between those terminals hasincreased to five units, that is to the value of condenser C5. The valueof the capacitance between the terminals X and Y can now be increasedfrom five to nine units, in single unit steps, by returning the fourswitches CA4CD4 one at a time to the unoperated condition. For instance,by returning switch CD4 to the unoperated condition, its associated unitcondenser C1 is connected in parallel with the S-unit condenser C5between the terminals X and Y. If now the remaining two-way switch CB5is returned to the unoperated condition, the condition of the unitssection returns to that shown in FIGURE 1 in which the value ofcapacitance between terminals X and Y is again zero. It will beappreciated therefore that the value of the capacitance connectedbetween the terminals X and Y is progressively variable from zero tonine units in unit value steps by the first nine switching operationsand can be returned to zero by the tenth switching operation. It willalso be appreciated that the switches lend themselves to be controlledby relays which can be energised to effect the first five steps of theprocess and released, that is de-energised, to effect the next fivesteps, so that the ten switching operations can be'controlled by meansof only tfive relays. During the first four steps the switches CA4-CD4can be operated in any order; similarly they may be released to returnto the unoperated condition in any order. The switches, however, can be,with particular advantage, controlled by a group of relays in theform ofa' free running relay counter and in such case it is preferred to causeall the relays to operate in the sequence 'CA4CD4, CBS and to return inthe same order to the unoperated condition.

The tens section can be operated similarly to the units section andprovides for the value of capacitance to be varied fromzero to ninetyunits in ten-units steps. In the process of increasing the capacitanceto a value in excess of ten units, the first and each subsequentswitching operation of the tens section is arranged to occur each timeswitch CES of the units section is returned to its unoperated condition.Moreover after each such operation all theswitches OF4-CI4, 015 of thetens section are required to remain unaltered during the next cycle ofoperation of the units section. The relay group for controlling thetens-section must therefore be dilferent from that for controlling theunits section. The relay arrangement to be described below will be suchas to cause the switches OF4-CI14, 0J5 to operate one at a time and inthat order and to be released in the order CI4-CF4, C15. After the unitsand tens sections have connected 99 units of capacitance between theterminals X and Y, the capacitancevalue can be increased by one unit bysimultaneously releasing switches CBS and C15 to the unoperatedcondition, thereby clearing the units and tens sections, and closingswitch CK4 in the hundreds section to complete the circuit between theIOU-unit condenser C100 and terminal Y. The switch CK4 will remainclosed during ten following cycles of operation of the units section andone cycle of the tens section, at the end of which 199 units of.capacitan cewill be connected between the terminals X and Y. It will beseen that by altering one switch of the tens-section after everyswitching cycle of the units section, and by closing thehundreds-section switch after the first switching cycle of the tenssection, the value of capacitance between the terminals X and Y can beraised in unit steps from 1 to 1-99.

Also, the range can be increased by one or more significant figures byinserting, in parallel with the sections described, one or more sectionssimilar to the units-section and with appropriate values of componentcondensers.

FIGURE 2. represents a system of relays for controlling the variablecapacitor which has been described with reference to FIGURE 1. Therehave been previously proposed several forms of apparatus forautomatically effecting, and printing the results of, tests on the quadsof telephone cables, in which each test involves the automaticadjustment of a capacity bridge and the result to be printed is theamount by which the variable arm of the bridge is adjusted to balancethe bridge. In such proposals, the variable arm of the bridge maycomprise a number of separate condensers which can be automaticallyconnected into the bridge network by a group of relays arranged to beenergised automatically one after another. The relays are provided withadditional contacts for selecting circuits to printing devices wherebythe value of the capacitance adjustment etfected by the relays can beautomatically recorded. Such an arrangement incorporates means which isresponsive to the condition of the bridge network'in such manner thatthe capacity adjusting action of the relays can be initiated andcontinued while the bridge is unbalanced and automatically stops when abalanced condition is achieved. Such means also ensures that the relayswhich have been energised will remain energised until released by othermeans. Such other means will include a device which automaticallyreleases the relays when the recording process is complete.

The arrangement herein described with reference to FIGURE 2 isapplicable in such a testing and recording system. For the purpose ofdescribing the present invention, it is only necessary to indicate thedevices which interconnect the capacity adjusting relays with the meanswhich is responsive to the condition of the bridge network and with themeans which is responsive to the completion of a recording.

The capacity adjusting relays comprise a units group of fi-ve relaysCA-CE, a tens group of live relays CF-CJ and a hundreds group comprisingone relay CK. There are also auxiliary relays PA-PB and PQ the purposesof which will be indicated below. The earth connection for energisingholding and releasing all the relays is taken from a bus-bar 1. Theearth connection to the bus-bar 1 is completed through a two-way switchPQ1 and normal closed contacts PMl. The contacts PMll are controlled bya relay or other means, not shown, which causes the contacts PM1 to openwhen a previous capacity value has been recorded, thereby releasing allthe capacity controlling and auxiliary relays. The central contact armof the two-way switch PQ1 is connected to earth by contacts i PMl. Theswitch PQ1 is controlled by an excess value relay PQ in such a mannerthat if the apparatus endeavours to increase the variable capacitybeyond the range provided by the apparatus, relay PQ is energised andswitch PQ1 is operated to break the earth connection to the bus-bar 1and to complete a holding circuit for relay PQ through an indicator lampL.

The earth connection to the units relays CA-CE is provided by a two-wayswitch P11 under the control of a relay, not shown, which is energisedwhen the bridge network, with which the illustrated apparatus is to beused, is unbalanced. In the FIGURE 2 the switch P11 is shown in theposition which corresponds to the bridge being in a balanced condition.Contacts PKl, shown open in FIG- URE 2, require to be closed to set therelay system in operation.

The units relays CA-CB are energisable one after another and in thatsequence from a relay-operating line 2 which can be connected to thebus-bar 1 through contacts PBZ, PC2, CB4 and PKl and switch P11. RelayPA causes the first unit relay CA to be energised by closing contactsPAZ. Relay CA operates make-before-break contacts CA1 to complete itsown holding circuit to the hold line 3, operates make-before-breakcontacts CA2- to prepare a similar holding circuit for the next unitsrelay CB and closes contacts CA3 to provide an energising connectionfrom the relay-operating line 2 through makebefore-break contacts CB1 torelay CB. The remaining units relays CC, OD and the five-units relay CEare associated with circuit and contact arrangements similar to relaysCA and CB. When relay CE is energised, its makebefore-break contacts CB2are operated to transfer the holding circuit for unit relay CA from thehold line 3 to the auxiliary hold line 4, and also contacts CB4 areopened to interrupt the operating earth connection to the relayoperating line 2. When relay CA releases the contacts CA2 are releasedto transfer the holding circuit for relay CB from the bold line 3 to theauxiliary hold line 4. The holding circuits for the remaining relaysCB-CB are similarly controlled. So long as the associated bridge networkis unbalanced the auxiliary hold line 4 is isolated, at switch P11, fromthe bus-bar 1 so that as soon as any relays are connected to the line 4they will be automatically released. When the bridge is balanced, switchP11 returns to the unoperated position as shown. This applies an earthto the auxiliary hold line 4, thus preventing the release of any relaysconnected to that :line, and interrupts the earth connection to therelay operating line. It will be seen therefore that the condition ofthe relays CA-CE of the units section is retained, after switch P11moves into the unoperated position, until the earth connection to thebus-bar 1 is interrupted at contacts PMIl or switch PQ1.

When relay CE operates it also closes contacts CB3 to initiate theoperation of a two-state pair of relays PB and PC. The purpose of thisrelay group is to initiate and control the cycle of operations of thetens group of relays CF-CJ. A change of state of the relay PB occurs forevery opening of contacts CB3, that is for every release of relay CE.When contacts CB3 are closed an earth is applied to the relay PC throughthe unoperated makebefore-break contacts PCI. Relay PC energises andoperates contacts PCI to apply its own holding earth connection tobusbar 1 and interrupt its energising circuit through contacts CB3.Contacts PC]. also complete an energising circuit for relay PB but thisis prevented from operating by a shunt circuit provided through contactsCB3 and FBI. When relay CE eventually releases, contacts CB3 open andinterrupt the shunt circuit of relay PB which is therefore energisedthrough contacts PCl. When relay CE next energises, during another cycleof the unitsrelay group, contacts CB3 close to short circuit relay PCthrough operated contacts PBl. Relay PC releases and contacts PCl returnto the unoperated condition in which the holding circuit for relay PB istransferred to operated contacts CB3. When relay CE eventually releases,contacts CB3 open to interrupt the holding circuit for relay PB whichtherefore releases and contacts PBl return to the unoperated condition.It will be seen therefore that with successive opening of contacts CB3,relay PB is alternately energised and de-energised.

The series circuit for initiating the operation of the units relay groupCA-CE includes a pair of two-way contacts PBZ and PC2. and it isapparent that this circuit can only be complete when both contacts areeither simultaneously operated or unoperated. When relay CE is firstenergised, contacts PC2 operate to interrupt that series circuit. Thisensures that no units relay energising circuit can be completed duringthe release of relays CA-CE in the second half cycle of operation of theunits relay group. When relay CB releases, contacts PBZ operate tocomplete the alternative series circuit through contacts PC2 and PB2 inpreparation for the initiation of the next cycle of operation of theunits relay group. The next time relay CB operates, contacts PC2 arereleased to again interrupt the series circuit and when relay CE .nextreleases contacts PBZ are also released so that the series circuit isagain completed by the return of contacts PBZ and PC2 to the positionshown in FIGURE 2.

The tens section of the variable capacitor is controlled by the tensgroup of relays CF-CJ which are energised one at a time and in thatOrder and are then released in the order CI-CF, CI. The arrangement issuch that one step in the change of state of the tens group. occurs atthe completion of each cycle of operation of the units group of relays,that is each time the last relay CE of the units group releases.

The tens group of relays CF-CI are divided into a group of odd numberrelays OF, CH, C] and a group of even number relays CG and CI. The oddnumber relays CF, CH and C] are energisable by a connection to earththrough two-way contacts PB4 in one position and an operating line 7which is interrupted at two positions by contacts C63 and C13. Similarlythe even number relays CG, C1 are energisable by a connection to earththrough the same contacts P134 in the other position and anotheroperating line 8 which is also interrupted in two positions by contactsCF3 and CH3. The energising circuit for each relay is completed bymake-before-break contacts which are operable by the energised relayitself to interrupt the energising circuit after completing a holdingcircuit. The contacts which operate in that manner are contacts CFl-CJI.Moreover neither of the operating lines 7 and 8 is extended, after theenergising of a relay from that line, to operate another relay from theline, until a further relay has been energised from the other line. Forinstance, after relay CF has been energised from line 7, relay CH cannotbe energised from line 7 until contacts CG3 have been closed by theenergising of relay CG from line 8. The two-way contacts PB4, controlledby relay PB and having the centre contact connected to the busbar 1,serve to apply the earth connection from the busbar to lines 7 and 8alternately. By this arrangement it is ensured that only one of the tensgroup of relays CF-CJ will be energised at the end of each cycle ofoperations of the units group of relays. When first energised, eachrelay CFCI will be held by a connection to a release line 5 or 6connected to the busbar 1 by contacts C12 in the case of line 5 andcontacts CM- in the case of line 6. Except in the cases of relays CI andOJ these holding circuits will be transferred direct to the busbar 1when a subsequent relay is energised. For instance, relay CF will beheld by its own contacts OF1 to line 5, until the energising of the'nextrelay CG transfers the holding connection direct to the busbar 1 throughcontacts CG2. Contacts CH2 and C12 are provided for a similar purpose inconnection with relays CG and CH. In the case of relay a holding circuitto busbar 1 will be prepared at contacts CFZ when the first relay, CF,of the group, is energised. In the case of relay CI it is not necessary,as will appear below, to transfer its hold connection from line 6.Two-way contacts CF3 interrupt the circuit from contacts PB4 to the evennumber relay operating line 8 until relay CF is energised and thiscannot occur until contacts P134 move to the operated condition at theend of the first cycle of the units relay group.

The functions of relay CI differ from those of the previously operatedrelays CF-CI of this group because, when relay CI is energised,provision has to be made for all five relays to release one at a time insequence, and for the hundreds relay CK to operate when relay CIreleases. Contacts C13 will open and remain open to render the contactsP34 ineffective so long as relay CI is energised. Relay PB also controlstwo-way contacts PB3 which operate simultaneously with contacts PB4 butwithout effect up to this stage. It will be seen that, in the upperposition, contacts PB3 connect one release line to the busbar 1; butwhen relay CI is not energised, there is a parallel connection at thecontacts C12 so that the connection between the line 5 and the busbar 1remains unaffected when contacts PB3 move into the lower position. Whilerelay CI is being energised, contacts PB3 will be in the lower position,and contacts C12 will move into the lower position so that the releaseline 5 will be disconnected from the busbar 1, but without effect onrelays CF and CH because their holding circuits will have beentransferred to the busbar 1 at contacts CGZ and C12. Also, in the lowerposition, contacts PB3 will have connected the release line 6 to thebusbar 1 before contacts C14 have opened to disconnect an alternativecircuit from the release line 6 to the busbar ll. This last mentionedswitching operation will be ineffective on relay CG because its holdingcircuit will have been previously transferred from the release line 6 tothe busbar 1 by contacts CH2. In the case of relay Cl, however the onlyholding circuit is tothe release line 6 through its own contacts C11. Itwill be seen from FIGURE 2 that when contacts PB3 are in the lowerposition they can also supply a' holding circuit from relay CI to' thebusbar 1 when contacts C11 are operated and contacts CFl are unoperatedbut so long as relay CF is energised this circuit will be interrupted bythe operated contacts CF2.

The arrangement of the tens group of relays is such that they will bereleased in sequence, upon successive operations of relay CE, in theorder CI, CH, CG, CF and CJ. The next operation of relay CE, after therelays in the tens group have been energised, causes contacts PB3 tomove into the upper position and interrupts the holding circuit forrelay Cl which was completed from the busbar 1 through contacts PB3 inthe lower position, release line 6 and switch C11. When contacts C12return to the unoperated position, the holding circuit for relay CH willbe transferred back to the release line 5 after this line 5 has beenconnected to the busbar 1 by contacts PB3 in the upper position. Whencontacts PB3 again move to the lower position, at the next operation ofrelay CE, the last mentioned holding circuit for relay CH isinterrupted. When contacts CH2 open, the holding circuit for relay CGwill be re-transferred to the release line 6 which is connected to thebusbar 1 by contacts PB3 in the lower position. At the next operation ofrelay CE, contacts PB3 will move into the upper position to break theholding circuit for, and so release, relay CG. The re-opcnin'g ofcontacts CGZ will retransfer the holding circuit for relay CF to therelease line 5 which in turn will be connected to the busbar 1 throughcontacts PB3 in the upper position. At the next operation of relay CE,contacts PB3 will again move into the lower position, and so will breakthe holding circuit for, and release, relay CF.

The arrangements for the release of relay C] are as follows. Althoughrelay CI is an odd number relay and is energisable from the same line 7as the other odd number relays CF and CH, its hold and release controlis effected through the release line 6 which is associated with the evennumber relays CG and CI. When relay CF is released, the holding circuitfor relay CI is transferred, by contacts CF2, from the busbar l to therelease line 6, so that when contacts PB3 next move to the upperposition, the earth is removed from the release line 6, so that relay CJreleases.

In the lower part of FIGURE 2 there is showna'two state relay pair PDand PE, which is similar to the previously described relay pair PB andPC. In the case of relays PD and PE, a change of state of relay PDoccurs every time relay CI, of the tens groups of relays, releases andreturns contacts CI'Z from the operated to the unoperated condition. Thesequence. of control and operation of the relay pair PD and PE isidentical with that of relays PC and PB, and in this respect it isimmaterial that contacts CJZ constitute a two-way switch. The relay pairPD and PE, by controlling the two-position contacts PDZ, serve toenergise relay CK when relay CI is first released, to connect theIOO-units capacitor C into the variable capacitor, and, if relay CI isreleased again in the same sequence of operations, to energise relay PQto indicate that the capacitance range of the apparatus has beenexceeded.

The operative steps to vary the value of capacitance,

connected between the terminals X and Y in FIGURE 1, from zero to 199units are as follows:

' With all the switches and contacts except PM in the condition shown inthe drawings, contacts PKl are closed. If the associated bridge networkis in an unbalanced condition, contacts P11 will be operated to energiserelay PA, close contacts PAZ and apply an earth to the first relay CA ofthe units group of relays. Relays CA, CB, CC and CD are energised insuccession to increase the capacitance value to 4 units; then relay CEis energised to add the S-unit capacitor C5 and remove the tour singlecapacitors. Relays CA-CD are now released in the same sequence toincrease the capacitance in unit steps to 9 units and eventually relayCE is released to return the capacitance value to zero.

When relay CE is released, relay PB is energised, and remains energised,to complete an operating circuit through contacts C13 and PB4 to thefirst relay CF of the tens group of relays. This relay'CF beingenergised inserts the -unit capacitor Cltl between terminals X and Y.The relay CF completes its holding circuit at contacts CPI and prepares,at contactsCFS an energising circuit for the next relay CG of the tensgroup of relays. While this operation has been in progress the followingconditions have been present to prevent premature operation of'the unitsgroup of relays. When the S-uni't'"capacitor-controlling relay CE wasenergised, contacts-CB4 opened to open the earth connection to the relayoperating line' 2. When CE was released, contacts CB4 reclosed, butcontactsPCZ were operated to maintain' the break in the earth connectionwhich was eventua'lly completed at contacts PBZ when relay PB operated.

To ensure that the first relay C1 of the tens group of relays willchange its state before the first relay CA in the units group isenergised, the energising of relay PA, which is now connected to earththrough contacts CB4, PC2. and PB2, is delayed by the capacitor Cconnected in parallel with the relay. The relay PA is not energised, sothat con tacts PA2 are not closed until the capacitor C has been chargedto the operation potential of the relay PA and this chargin period ismade longer than the time required for the first relay CF of the tensgroup of relays to be energised when contacts PR4 are moved into theoperated position.

The complete cycle of operations of the units group of relays is nowrepeated and when relay CE again releases, the contacts PB4 return tothe lower position to energise the second relay CG of the tens group ofrelays. These operations continue until there is obtained the conditionin which 59 units of capacity are connected between the terminals X andY. In this condition all the relays of the units group have beenreleased with the exception of relay CE, and all the relays of the tensgroup are energised. Relay CE now releases causing contacts PB3 to moveto the upper position and causing relay CI, in the tens group, to bereleased because contacts C14 have been opened by the energisation ofrelay C1. The value of capacitance has now been increased to 60 units.The cycle of opera-- tions is again repeated causing relays CH, CG, CFof the tens group to be released one at a time and in that order.

-When the value of inserted capacitance has become 99 units, relay CE ison the point of being released and when this occurs relay C1 in the tensgroup is also released.

When relay C1 was energised, contacts C12 moved into the lower positionto complete an energising circuit for relay PE which in turn completedits holding circuit at contacts PEI. Although contacts PEI complete anenergising circuit tor relay PD, this is short circuited throughcontacts PD1 and C12. When relay C1 is eventually re leased, contactsC12 return to the upper position thus removing the short circuit fromrelay PD which is energised. This changes over contacts PDZ to energisethe IOO-unit relay CK which completes its holding circuit at contactsCK1 and connects the 100-unit capacitor C100 between the terminals X andY.

The relays PD, PE and CK remain energised while the complete cycle ofoperations of the units group and tens group of relays is repeated. Atthe end of that complete cycle 199 units of capacitance are insertedbetween the terminals X and Y. The apparatus will not increase thisvalue of capacitance. When relay C1 was energised for the second time itapplied, through contacts C12 and PD1, a short circuit to relay PE whichwas consequently released. Relay PD was not released because the returnof the make-before break contacts PEI provided a holding circuit for therelay through contacts C12. In the event of the cycle of operations ofthe units group of relays tending to be repeated this will immediatelyresult in the release of relay C1 causing the holding circuit for relayPD to be broken at contacts C12. Contacts PD2 are thus returned to thenon-operated condition and provide an energising circuit for relay PQthrough the closed contacts CK2. As previously indicated the contactsPQl are altered to provide a holding circuit for relay PQ through theindicator L and to release all the other relays.

It is required to ensure that, when relay CK is to be energised toconnect the IOU-unit capacitor C between terminals X and Y, theinitiation of the next cycle of operation of the units group of relayswill be delayed until that step has been completed by the closing ofswitch CK l. This can be provided for by short-circuiting the relay PAthrough contacts CK3, PB2, CF3, P134 and C13. In the unoperatedcondition as shown in FIGURE 2 the short circuit is incomplete atcontacts CK3 and PE2. The energising of relay C1, at the end of thefirst half-cycle of operation of the tens group of relays, will energiserelay PE, as described above, and thereby change the state of contactsPEZ so as to tend to complete the short circuit for relay PA. However,at this stage, the energising of relay CF has provided another break inthe short circuit at con tacts CPS and also the energising of relay C1has opened contact C13 to provide another break. When the circuit forreleasing relay C1 is just completed, relay OF has already been releasedso that contacts CF3 are again in the position shown, and contacts PB4are also in the position shown. The contacts C13 close, when relay C1actually releases, to complete the short circuit for relay PA. The shortcircuit is eventually opened when relay CK is energised and changes overthe contacts CK3. The cycle of operations of the units group of relaysthen recommences by the energising of the first relay CA after the timedelay provided by the capacitor/ resistance circuit associated with therelay PA.

If at any time the bridge-network, incorporating the variable capacitor,becomes balanced, contacts PI]; will revert to the position shown inFIGURE 2, the earth connection will be removed from the relay operatingline 2, so that any non-energised relays of the units group will remainin that condition, and the release line 4 will be connected to earth, bycontacts P11, so that any energised relays of the group will be held inthat condition. No further changes of state of the tens group of relaysCF-CJ nor of the hundreds relay CK can occur, because all such changesof state are only initiated by the release of the units group relay CE.

FIGURE 3 illustrates a variable resistor which can be controlled by thegroup of relays already described with reference to FIGURE 2, to providebetween terminals X and Y a value of resistance which is variable inunit steps from zero to 199 units.

In FIGURE 3 the two-way switches RCA4-RCD4, RCES, RCFd-RCM, ROI 5 andRCK4 correspond in number and in their order of operation to the two-wayswitches already described with reference to FIGURE 1. By changing-overswitches RCA4-RCD4 one at a time and in that order the resistanceinserted between the terminals X and Y is increased in unit steps fromzero to 4 units. By then changing over switch RCES the resistance valueis increased to 5 units. Bythen restoring to the initial conditionswitches RCA4-RCD4 one at a time and in the same order the value ofresistance is increased in unit steps from to 9 units. The nextswitching operation, comprising returning switch RCES to the initialcondition restores the value of the inserted resistance to zero. Bymeans of the relay arrangement already described the final switchingmovement of the units section is accompanied by the first switchingmovement of the tens section. In this section the operation of theswitches RCF4-RCI4 one at a time and in that order raises the resistancebetween terminals X and Y from zero to 40 units in tenunit steps. Bychanging over switch RCJS the value of the inserted resistance isincreased to 50 units and by then releasing the first four switches ofthis section one at a time and in the order RCI4-RCF4 the resistance isincreased to 90 units. Then by returning switch RG15 to the initialcondition the resistance is again reduced to zero except that, by meansof the relay arrangement already described, switch RCK4 is operated toinsert 100 units of resistance into the circuit.

Although the number of switches used in the variable resistance is thesame as that in the variable capacitor other modifications of thecircuit are required due to the essentially difierent natures of theimpedance elements. For instance in the variable capacitor thecapacitance is changed by altering the number of unit capacitorsconnected in parallel whereas in the variable resistor the re sistanceis altered by changing the number of the unit resistors connected inseries. a I

In the arrangement shown in FIGURE 3 the movable contacts of theswitches controlling the unit resistors R1 are permanently connected toone terminal X to which is also permanently connected one end of each oftwo sets of four series connected unit resistors R1. The other end ofone of these series connected sets of unit resistors is permanentlyconnected tothe side contacts a of the first switch RCA4- and the lastswitch RCES. The side contacts a of the remaining three switchesRCB4-RCB4 are permanently connected to intermediate points between thoseunit resistors in such a way that between each adjacent side contacts athere is permanently connected a unit resistor R1. The other sidecontact b of the first switch RCA i is permanently connected to theotherwise free 'end of the second set of series connected unit resistorsR1 and the side contacts b of the three switches RCB4- RCB4 arepermanently connected to intermediate points in the set in such a waythat a single unit resistor R1 is connected between each pair ofadjacent side contacts b. The arrangement is. also such that there is aunit resistor R1 connected between the side contact a of the fourthswitch RCB4 and the terminal X and also another unit resistor R1connected between the side contact b of that switch and the terminal X.A S-unit resistor R5 is connected between the side contacts b of thefirstswitch RCA4 and the fifth switch RCES. The movable contact of thefifth switch RCES constitutes the other terminal of this units section.In the unoperated condition, shown in FIGURE 3, there is a short circuitbetween. the two terminals through the movable contact and side contacta of switch RCESand the side contacta and movable contact of the firstswitch RCA4. The first step, eifected by the energizing of relay CA inFIGURE 2, comprises the movement of the central contact of switch RCA4out of engagement withits side contact a and into engagement with itsside contact b. This removes a short circuit from the unit resistor R1connected between the side contacts a of the switches RCA4 and RCB4 sothat this resistor is now connected in series between the terminals 12RCA4 which itself short circuits the set of four series connected unitresistors R1 of which one end is connected to the side contact b ofswitch RCA4. By re turning switches RCA4-RCD4 one at a time and in thatorder to their unop-erated condition the last mentioned set of unitresistors R1 are brought one at a timeinto the series circuit betweenthe terminals of the section. The final return of RCES to its initialconnection breaks that series circuit and recloses the short circuitthrough its side contact a and the side contact of the first switchRCA4.

The tens section of the variable resistor diifers from the units sectionin the following respects. In place of the unit resistors R1 there. arenow used IO-unit resistors R10 and a 50-unit resistor R50 is used inplace of the 5- unit resistor R5. Whereas in the unit section the S-unitresistor R5 was connected between the side contacts b of switch RCES andthe first switch RCA4, the SO-unit resistor R50 in the tens section isconnected between the side contacts b of the fifth switch RCJS and thefourth switch RCI4. Furthermore, the part circuit containing a unitresistor R1 connected between the terminal X and the si-decontact b ofthe fourth switch RCD4 in the units section has no counter-part in thetens section, but a 10-unit resistor R10 is permanently connectedbetween the corresponding terminal of the tens section and the sidecontact b of the first switch RCF4. It 'will be seen that thearrangement of the switches and separate resistors in the tens sectionis such that the resistance between the two terminals of this section,that is between the centre contacts of switches RCES and RCJ5, will beincreased in IO-unit steps from zero to units by moving the switches oneat a time into the operated condition in the order RCF4'-RCI4 and RCJ5and thereafter returning the first four switches into the unoperatedcondition in the order of RCI4-RCF4. By thereupon returning the switchRG15 into the non-operated position the inserted resistance is again atzero. It will also be seen that this sequence of switching operationscan be efiected by the tens group of relays already described withreference to FIGURE 2.

Finally the hundreds section of the variable resistance comprises a l00unit resistor R short circuited by a normally closed switch RCK4. Thiscan be operated by means of the relay CK in the hundreds section of thearrangement shown in FIGURE 2 to remove the short circuit from theresistor R100 and thus insert a IOU-unit of resistance between theterminals X and Y of the variable resistance. 7

Both the variable capacitor and resistor can be expanded to cover arange of values extending overmore than three significant figures byadding one or more sections corresponding in each case to the tenssection. Each such added section, which will be series connected withthe other sections in the case of the variable resistance and parallelconnected in the case of the variable capacitor, will include units ofresistance or capacitance appropriately related to its position inrelation to the other sections. Each such added section can becontrolled by a group of relays which is similar to the tens sectiongroup of relays which has been described. I

A variable inductance can be constructed in a manner similar to that ofthe variable resistance, the resistors being replaced by screenedinductances and the relay controlling arrangements remaining the same.

One advantage of the improved variable impedance lies in the use of anarrangement of switches which is such that the full range of adjustmentis obtainable by a cycle of switching operations at the end of which thedevice is returned to the initial condition by a simple switchingoperation instead of it being necessary to reset a comparatively largenumber of switches to an initial condition. In combination with thatadvantageis the factthat a comparatively small number of switches arerequired and the numher and type of such switches are particularly.adapted for automatic control by groups of relays. In the case of 13 thevariable capacitor, there is the added advantage that only acomparatively small number of fixed-value condensers is required. In allthe cases described, variation through a range of ten equal value stepsis obtainable with only five relay-operated switches and in the case ofthe variable capacitor only five fixed-value condensers are required.

What I claim as my invention is:

1. A variable impedance comprising A(N1) separate equal-valueimpedances, where A is a whole number less than 3 and N is any wholenumber greater than unity, and a separate impedance of N-times thatvalue, N twoway switches of which each switch comprises a first sidecontact and a second side contact and a central movable contact which isin conductive engagement with the first side contact in an unoperatedcondition of the switch and with the second side contact in an operatedcondition of the switch, each of Nl of the two-way switches controllingthe insertion of the value of one of the smaller separate impedances incircuit between two terminals of the variable impedance and the Nthtwo-way switch controlling the insertion of the value of the largerseparate impedance between those terminals, and the switch contacts andseparate impedances being interconnected with the two terminals toprovide for the total value of impedance in circuit between the twoterminals to be progressively varied in 2Nl equal-value steps from aminimum to a maximum value by 2N-1 changes of conditions of the switchesand to be returned to the minimum value in the next 2Nth step by asubsequent change of condition of one of the switches, the 2N changes ofcondition of the switches comprising a change of state of all theswitches one at a time in succession to the operated condition andthereafter one at a time to the unoperated condition.

2. A variable impedance comprising N 1 separate equal-value impedances,where N is any whole number greater than unit, and an Nth separateimpedance of N times that value, N two-way switches of which eachcomprises a first side contact and a second side contact and a centralmovable contact which is in conductive engagement with the first sidecontact in an unoperated condition of the switch and with the secondside contact in an operated condition of the switch, a permanentconnection between all the first side contacts of Nl of the switches,the second side contact of the Nth switch and one terminal of the largerseparate impedance, a second permanent connection between the remainingside contacts of all the switches, a third permanent connection betweenthe second terminal of the larger separate impedance and one terminal ofeach of the smaller separate impedances, and N -l permanent connectionseach joining the second terminal of one of the smaller impedances to thecentral contact of one of the said N-1 of the switches, whereby thetotal value of the impedances connected in parallel between the centralcontact of the Nth switch and the said third permanent connection isprogressively variable in 2N-1 equal-value steps from a minimum to amaximum value and in the next 2Nth step to the minimum value by changingthe state of all the switches one at a time in succession to theoperated condition and thereafter one at a time to the unoperatedcondition.

3. A variable impedance comprising 2(N-1) separate equal-valueimpedances, where N is any whole number greater than unit, and separateimpedance of N times that value, permanently connected in the form of afirst and a second series chain of N 1 of the smaller impedances withthe larger impedance at the end of the second chain, N two-way switcheseach comprising a first side contact, a second side contact and acentral contact which is in conductive engagement with the first sidecontact in an unoperated condition of the switch and with the secondside contact in an operated condition of the switch, a first permanentconnection between one end of each chain of 14 impedances and thecentral contacts of N l of the switches, a first set of permanentconnections each between the first side contact of one of N 1 of theswitches and a point between two adjacent smaller impedances in thefirst chain, and a second set of permanent connections each between thesecond side contact of one of said N l of the switches and a pointbetween two adjacent smaller impedances in the second chain, a secondpermanent connection between the first side contacts of one of said N lof the switches and of the Nth switch and a third permanent connectionbetween the second side contact of the Nth switch and the terminal ofthe larger impedance at the end of the second chain, whereby the valueof the impedances connected in series between the central contact of theNth switch and the said first permanent connection is progressivelyvariable in ZN-l equal-value steps from a minimum to a maximum value andin the next 2Nth step to the minimum value by changing the state of allthe switches one at a time in succession to the operated condition andthereafter one at a time in succession to the unoperated condition.

4. A variable impedance comprising A(Nl) separate equal-value impedanceswhere A is a whole number less than 3 and N is any whole number and aseparate impedance of N-times that value, N two-way switches eachcomprising a first side contact and a second side contact and a centralmovable contact which is in conductive engagement with the first sidecontact in an unoperated condition of the switch and with the secondside contact in an operated condition of the switch, each of N 1 of thetwo-Way switches controlling the insertion of the value of one of thesmaller separate impedances in circuit between two terminals of thevariable impedance and the Nth two-way switch controlling the insertionof the value of the larger separate impedance between those terminals,and the switch contacts and separate impedances being interconnectedwith the two terminals to provide for the value of impedance in circuitbetween the two terminals to be progressively varied in 2N-1 equal-valuesteps from a minimum to a maximum value and to be returned to theminimum value in the next 2Nth step by changing the state of all theswitches one at a time in succession to the operated condition andthereafter one at a time to the unoperated condition, and there beingprovided a chain of N relays, the central contacts of the two-wayswitches being movable to the operated condition by energization of saidrelays, and said relays being energizable one after another insuccession to produce the first N changes of state of the switches andbeing releasable one after another in succession to produce the second Nchanges of state of the switches.

S. A variable impedance comprising A(N1) separate equal-value impedanceswhere A is a whole number less than 3 and N is any whole number greaterthan unity, and a separate impedance of N-times that value, N twowayswitches each comprising a first and a second side contact and a centralmovable contact which is in conductive engagement with the first sidecontact of the switch in an unoperated condition and with the secondside contact of the switch in an operated condition, each of Nl of thetwo-way switches controlling the insertion of the value of one of thesmaller separate impedances in circuit between two terminals of thevariable impedance and the Nth two-way switch controlling the insertionof the value of the larger separate impedances between those terminals,and the switch contacts and separate impedances being interconnectedwith the two terminals to provide for the value of impedance in circuitbetween the two terminals to be progressively varied in 2N 1 equal-valuesteps from a minimum to a maximum value and to be returned to theminimum value in the next 2Nth step by changing the state of all theswitches one at a time in suctwo-Way switches being movable to theoperated condition by energization of said relays, said relays beingenergizable one after another in succession to produce the first Nchanges of state of the switches and being releasable one after anotherin succession to produce the second N changes of state of the switches,and those of said relays of state being releasable in the reverse orderto produce the N-l-lth to 2N1th changes of state.

References Cited in the file of this patent which are energizable toproduce the first N-1 changes 10 2,762,038

UNITED STATES PATENTS Howe Aug. 17, 1920 Eaves Apr. 22, 1924 Bush June26, 1956 Lubkin Sept. 4, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,036,263 May 22, 1962 Lister Hallas It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 2, line 3, for "imperdance" read impedance -5 column 3, lines 61,62, 63, and 68, column 4, lines 7, l9, and 64, column 9, lines 20, 73,and 74, column 10, line 22, and column 12, lines 15 17, 24, 42, and 46,for "-unit", each occurrence, read -units column 4, line 57, for "CF4-CI 14" read CF4-CI4 column 9, line 59, for "CG, read CG and column 13,lines 37 and 66, for "unit", each occurrence, read unity Signed andsealed this 9th day of October 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

